WotC made a Knights of the Old Republic Campaign Guide for SAGA Edition.
More than a decade prior to that, West End Games made the Tales of the Jedi Companion for the old d6 Star Wars RPG. Tales of the Jedi was a comic book series set a few decades before the KOTOR games, and was the first look at that era, and that was the first Star Wars RPG book to really step away from era of the films and what immediately happened after.
Basically technology is roughly the same. Remember, the Galactic Republic was founded ~25,000 years before the films, and there were older Empires than that (the Hutt Empire and the Rakata most famously). Generally, technology from the films exist, but is either new (like astromech droids), or is ancient and been around for many millennia but notably weaker than what existed later (hyperdrives, lightsabers, most droids, blasters).
The main differences in technology, from a gaming perspective, from the epoch of the films to the ~4,000 BBY era of KOTOR and the Tales of the Jedi comics (taking notes from both books):
1. Hyperdrives are much slower. Multiply all hyperdrive modifiers by 3 or 4. Most ships have x6 to x8 hyperdrives, with the fastest military and smuggling ships getting x4 or maybe x3. Backup hyperdrives, if used at all, can be x24 or even slower. For over 20,000 years a network of hyperspace beacon satellites have made safe hyperspace travel a reality, leading to wars to protect or control this network of navigational beacons. Now, breakthroughs in miniaturized sensor and computing technologies are leading to more portable navigational computers and astromech droids allowing starships to plot their own routes. Remember that in the era of the films, starfighters with their own hyperdrives were expensive and uncommon, and they are virtually unheard of in this era.
2. Droids need more time to recharge, more on the scale of like a human needing to sleep. We only saw C-3PO in the films need to "close down for a while" once. Due to less efficient processors and power supplies, droids needed as much rest, maybe just a little less, than organics.
3. Weapons are a little weaker. Instead of "blasters", the "pulse wave blaster" is the typical small arm, which has a shorter range and tends to be bulkier and more power-consuming, even if of comparable destructive strength. Most lightsabers are not as strong. Converting the dice over, most lightsabers would do 2d6 instead of 2d8, because of inferior crystals from the Adegan system (the best widely available at the time). The crystals to make "modern" lightsabers exist, but are rare and difficult to find. Only later discoveries of better sources of crystals (like the Crystal Caves of Ilum) and the Sith improving crystal synthesis technologies for their signature red crystals would make 2d8 lightsabers standard.
4. The Holonet does not exist, it has not been built yet. While subspace communications keep the Republic (and when it exists, the Sith Empire) together, the vast wide bandwidth of the Holonet providing real-time communications, entertainment, and information exchange of the late Republic does not exist. The galaxy is connected more like Earth circa 1910 with telegraphs making international communications and radio for important relatively short-range traffic, instead of the modern internet and satellite communication providing instant connectivity worldwide.
5. The galaxy is a smaller place. Not literally, but it's a lot less explored and scouting the hyperlanes is big business. Wild Space hasn't been discovered yet, and the Outer Rim Territories are the very edge of space and a lot of Outer Rim worlds known in later eras like Tatooine or Dac (a.k.a. Mon Calamari) are either undiscovered, or brand new discoveries.
6. A lot of races haven't been discovered yet, and others are brand new. No Ssi'ruuvi, no Chiss. The planet Dac was just discovered only a century or so ago, so Mon Calamari and Quarren are uncommon and new on the galactic scene. Kashyyyk has just been discovered within the last few years, away from charted Republic space, and the Czerka corporation has been enslaving wookiees claiming them to be non-sentient beasts of burden to get around Republic anti-slavery laws (proving their sentience and winning their freedom in this era is a story that has not been told). The Yuuzhan Vong invasion is thousands of years off, and there is only a single wild story that indicates that just maybe the first scout ship arrived in the galaxy around this time, maybe.
